The researchers aimed radiation from the Linac Coherent Light Source (LCLS), located at the Stanford Linear Accelerator Center (SLAC), at a cell containingneon gas, setting off an avalanche of femtosecond-duration
X-ray emissions to create a new “atomic X-ray laser” in the kiloelectronvolt energy regime.

“X-rays give us a penetrating view into the world of atoms and molecules,” said physicist Nina Rohringer, a former LLNL postdoc, now a group leader at Max Planck Society’s Advanced Study Group. She collaborated with researchers from SLAC, LLNL and Colorado State University.

The new laser fulfills a 1967 prediction, which proposed that X-ray lasers could be made by first removing inner electrons from atoms and then inducing electrons to fall from higher to lower energy levels, releasing a single color of light in the process. But until 2009, when LCLS turned on, no X-ray sources were powerful enough to create this type of laser.

To make the atomic X-ray laser, LCLS’s powerful X-ray pulses — each a billion times brighter than any available before — knocked electrons out of the inner shells of many of the neon atoms. When other electrons fell in to fill the holes, about one in 50 atoms responded by emitting a “hard X-ray,” which has a very short wavelength (1.46 nanometers). Those X-rays then stimulated neighboring neon atoms to emit more X-rays, creating a domino effect that amplified the laser light 200 million times.

It may be useful for high-resolution spectroscopy and nonlinear X-ray studies.

In the future, Rohringer says she will try to create even shorter-pulse, higher-energy atomic X-ray lasers using oxygen, nitrogen or sulfur gases.